Superhydrophobic coatings for deposit reduction in selective catalytic reductant systems

Abstract

Superhydrophobic coatings to reduce deposit formation of diesel exhaust fluid (DEF) within selective catalytic reduction (SCR) systems.

The invention claimed is: 
     
       1. A method for reducing deposits on the internal surface of SCR component(s) comprising:
 providing an SCR component having an internal volume and internal surface and creating a vacuum within the interior volume of the SCR component; 
 supplying gas to the interior volume of said SCR component wherein the gas includes a plasma precursor in the gas phase; 
 biasing the SCR component to ground; 
 forming a plasma along the length of said SCR component; 
 generating positive ions of said plasma precursor which are deposited on the internal surface of said SCR component; 
 forming a coating on said internal surface of said SCR component wherein said coating exhibits a water contact angle in oil of greater than 120°. 
 
     
     
       2. The method of  claim 1 , wherein said plasma precursor comprises hexamethyldisiloxane. 
     
     
       3. The method of  claim 1  wherein said plasma precursor comprises a perfluorinated propylene oxide. 
     
     
       4. The method of  claim 1  wherein said plasma precursor comprises a substituted tetramethylenedisiloxane (sTMDSO) precursor: 
       
         
           
           
               
               
           
         
         wherein R 1  and/or R 2  are selected from a carbon-hydrogen alkyl group wherein one or more of the carbon-hydrogen atoms in the alkyl group may be replaced by a carbon-fluorine linkage and wherein said sTMDSO precursor is introduced at a flow rate (Q sTMDSO ); and 
         a perfluorinated propylene oxide (PFPO) precursor: 
       
       
         
           
           
               
               
           
         
         wherein R 1  and/or R 2  may a F atom or a perfluorinated alkyl group wherein said perfluorinated propylene oxide precursor is introduced at a flow rate (Q PFPO ) and setting a flow rate ratio (Q sTMDSO /Q PFPO ) in the range of 0.1 to 2.0 (g/(hr·sccm)). 
       
     
     
       5. The method of  claim 1 , wherein said coating comprises 50 to 60 atomic percent carbon, 20 to 30 atomic percent oxygen and 15 to 25 atomic percent silicon. 
     
     
       6. The method of  claim 1 , wherein said coating, at a depth of up to 300 Angstroms, comprises the following bond types:
 (a) Si—O— at a relative concentration of 38.5(±12) %; 
 (b) Si—C at a relative concentration of 25.6 (±5) %; 
 (c) C—O at a relative concentration of 4.5 (±3) %; and 
 (d) C—C at a relative concentration of 31.4 (±2) %. 
 
     
     
       7. The method of  claim 1 , wherein said coating has a thickness of up to 5.0 μm. 
     
     
       8. The method of  claim 1 , wherein said coating has a water contact angle in oil of greater than 120° to 170°. 
     
     
       9. The method of  claim 1 , wherein said coating has a water contact angle in oil of greater than 155°. 
     
     
       10. The method of  claim 1  wherein said coating comprises a fluoro-organsiloxane coating. 
     
     
       11. The method of  claim 1 , wherein said SCR component comprises metallic tubing. 
     
     
       12. The method of  claim 1 , wherein said SCR component comprises a mixer. 
     
     
       13. The method of  claim 1 , wherein said SCR component comprises a DEF injector. 
     
     
       14. A coated SCR component comprising:
 a SCR component having an internal surface configured to be exposed to diesel emission fluid; 
 a carbo-siloxane coating disposed on said SCR component internal surface, wherein said coating has a water contact angle of greater than 120°, wherein said coating comprises 50 to 60 atomic percent carbon, 20 to 30 atomic percent oxygen, and 15 to 25 atomic percent silicon, wherein said coating, at a depth of up to 300 Angstrom, comprises: (a) Si—O— at a relative concentration of 38.5(±12) %; (b) Si—C at a relative concentration of 25.6 (±5) %; (c) C—O at a relative concentration of 4.5 (±3) %; and (d) C—C at a relative concentration of 31.4 (±2) %. 
 
     
     
       15. The coated SCR component of  claim 14 , wherein said coating ha a water contact angel in oil of greater than 120° to 170°. 
     
     
       16. The coated SCR component of  claim 14 , wherein said coating is present at a thickness of up to 5.0 μm. 
     
     
       17. The coated SCR component of  claim 14 , wherein said coating comprises 56 to 57 atomic percent carbon, 20 to 26 atomic percent oxygen, 17 to 23 atomic percent silicon. 
     
     
       18. The coated SCR component of  claim 14 , wherein said coating is present at a depth of up to 200 Angstroms. 
     
     
       19. The coating SCR component of  claim 14 , wherein said coating is present at a depth of up to 100 Angstroms.